Visual displays for data processing apparatus, such as computers, are normally field emission displays of the cathode ray tube type. These generally have a depth of the order of their size dimension, which conventionally is their corner to corner or diagonal dimension. This depth can render them inconvenient in use. Recently, laptop computers have become increasingly widely used. These incorporate a “flat” screen display, usually of the liquid crystal type.
Proposals have been made to provide displays having flat screen cathode ray tubes. These are known as Spindt cathodes, after the inventor of U.S. Pat. No. 3,755,704. In this specification, they are referred to as field emission devices.
In our International applications Nos WO 99/17329 & -30, our earlier International Applications, we described an improved “flat” screen visual display having a field emission device and in particular an improved method of sealing the display.
Essentially the visual display comprises:                at least one field emission device including an emission layer on a substrate;        a glass face plate carrying excitable phosphor material; and        fused sealing material peripherally sealing the face plate to the emission device(s),        whereby the face plate is parallelly spaced from the emission layer.Herein, this visual display is referred to as “the Defined Visual Display”.        
Essentially the method of sealing the Defined Visual Display consists in the steps of:                evacuating the display, to evacuate the space between the emission layer and the face plate; and        irradiating a peripheral region of the face plate to fuse the sealing material, thereby sealingly securing the face plate to the emission device(s).Herein, this sealing method is referred to as “the Defined Sealing Method”.        